▎ 摘　　要

High electrochemical performance is important to achieve practical application of energy storage devices. It has been found recently that it is hard to achieve high capacity and high stability simultaneously using a single electrode material. Thus, constructing composite electrode materials which can combine the advantages of different materials together is an efficient approach to improve the electrochemical properties. In this work, we have built a vacancy-rich MnO2-x/reduced graphene oxide (rGO) composite film through a facile one-step route. In the synthesis process, GO nanosheets were reduced into rGO to improve the electronic conductivity, while Mn2+ was oxidized to MnO2 with vacancies. The obtained vacancy-rich MnO2-x/rGO composite showed a superior electrochemical performance: The specific capacitance reached 675.5 F/g at a current density of 0.5 A/g and the material demonstrated high capacitance retention (96.1 % after 10000 cycles). Besides, the symmetric electrochemical capacitor based on the vacancy-rich MnO2-x/rGO composite electrode can achieve a high energy density (8.42 mWh/cm(3)) and power density (3.78 W/cm(3)) as well as excellent stability.